Hiroshi Maeta

Synchrotron radiation beamline to study radioactive materials at the Photon factory

Abstract Design and construction of a new beamline have been described. The beamline is housed in a specially designed area controlled for radioactive materials at the Photon Factory (PF) in the National Laboratory for High Energy Physics (KEK). The beamline system consists of a front-end and two branchlines. One of the branchlines is used for X-ray photoelectron spectroscopy and radiation biology in the energy range of 1.8-6 keV and the other for X-ray diffractometry and XAFS studies as well as radiation biology in the range of 4–20 keV. The former was particularly equipped for the protection against accidental scattering of radioactive materials both inside and outside of the vacuum system.

Raman spectra of neutron-irradiated pyrolytic graphite

Abstract Raman spectra of pyrolytic graphite after neutron irradiation at 5°K and annealing up to room temperature have been studied by a laser Raman spectrometer. In addition to the omnipresent line at 1580 cm-1, a Raman line have been observed at 1623 cm-1 which can be ascribed to C2 molecules. Another line has also been observed at 1361 cm-1, already reported in ground graphite, carbon blacks and activated carbons. This line is discussed in relation to point defects produced by neutron irradiation.

Thermal Expansion Coefficient of Synthetic Diamond Single Crystal at Low Temperatures

The lattice parameter of synthetic diamond single crystals has been measured in the range 4.2-320 K by the X-ray diffraction method. The lattice parameter is found to be nearly constant between 4.2 and 90 K. The thermal expansion coefficient α calculated from the experimental results is very small (of the order of 10-7 or less) and no definite evidence of the negative thermal expansion is found within our relative experimental accuracy of the order of ±1×10-6.

c-Axis Spacing Changes in Pyrolytic Graphite after Neutron Irradiation at 5 K

Change in the c -axis spacing in pyrolytic graphite after fast neutron irradiation at 5 K and subsequent isochronal pulse annealings have been measured in the range of 5∼900 K by X-ray diffraction method. The c -axis expansion was estimated to be Δ c 0 / c 0 =3.4 N i , where N i is the fractional concentration of interstitial atoms. This corresponds to a volume change of 3.3 atomic volume per interstitial atom. For annealings of the c -axis spacing, a small recovery below 80 K was followed by a large recovery at around 100 K, and above it a small continuous recovery occurred up to 900 K. The large recovery at around 100 K was interpreted by the formation of C 2 molecules and interstitial clusters. The present results were discussed comparing with the so far reported results of electrical resistivity, thermal resistivity and stored energy release measurements.

Grain size measurement of nanocrystalline gold by X-ray diffraction method

Abstract The X-ray diffraction profiles on nanocrystalline gold prepared by the gas deposition method were studied by Warren-Averbach and integral breadth analysis for the evaluation of grain sizes and internal strains. The grain size of as-prepared specimens, estimated by Warren-Averbach analysis, was in the range of 7 to 20nm. The thermal stability of these specimens was found to be quite high; when annealed for 1h, the grain size remained unchanged up to 770K and grew about twice at 1070K. The root mean square strain, estimated by integral breadth analysis, was in the range of 0.8–2.3 × 10−3 and reduced to ~3 × 10−4 after annealing at 870K and higher.

Recovery of Fast Neutron Irradiated Copper and Gold at Low-Temperatures

The recovery of the electrical resistivity of 99.999% purity Cu and Au and Au-0.1% Cu alloy was studied after fast neutron irradiation at liquid He temperature. The damage production rate decreased by cold work and alloying in Au, but it increased by cold work in Cu. Cold work enhanced the recovery above 150°K in Cu and above 50°K in Au. In Au, the stage III recovery shifted by about 30°K toward lower temperature for cold worked specimens.

Recovery of Fast Neutron Irradiated Iron at Low Temperatures

The isochronal annealing studies of electrical resistivity of Fe after fast neutron irradiation at liquid helium temperature were performed. Recovery spectra of annealed, cold worked and as-received specimens were compared. The main peak in stage I was divided into two substages and stages II and III recovery seemed to be influenced by interstitial impurities.

ELECTRONIC EXCITATION EFFECTS IN ION-IRRADIATED HIGH-TC SUPERCONDUCTORS

Abstract We have measured the fluence dependence of the c -axis lattice parameter in EuBa 2 Cu 3 O y (EBCO) irradiated with various ions from He to Au over the wide energy range from 0.85 MeV to 3.80 GeV. We have observed a linear increase of the c -axis lattice parameter with increasing fluence for all irradiations. The slope of c -axis lattice parameter against fluence, which corresponds to the defect production rate, is separated into two contributions; the effect via elastic displacement and the effect via electronic excitation. The former contribution exhibits a linear increase against the nuclear stopping power, S n . The latter contribution is scaled by the primary ionization rate, d J /d x , rather than by the electronic stopping power, S e , and is nearly proportional to (d J /d x ) 4 .

First results from the crystal structure analysis beamline at SPring-8.

Results from the first measurements at the crystal structure analysis beamline (BL02B1) at SPring-8 are presented. The capabilities of this beamline are also discussed.

Thermal expansion of a boron-doped diamond single crystal at low temperatures

The lattice parameter of a single-crystal boron-doped synthetic diamond has been measured in the range 4.2-300 K by x-ray diffraction (Bond method), with precision . Over the whole range the results are consistent with A, where T is the absolute temperature. The dilation due to doping indicates a boron concentration of about 100 ppm. The increase of thermal expansion over that of an undoped synthetic diamond is found to be unexpectedly large (10-15%), giving an apparent dilation on doping that is markedly temperature dependent.